Distributed radio transparent clock over a wireless network

ABSTRACT

An example method comprises receiving, by a first PHY of a first transceiver, a timing packet, timestamping, by the first transceiver, the timing packet and providing the timing packet to a first intermediate node, determining a first offset between the first intermediate node and the first transceiver, updating a first field within the timing packet with the first offset between the first intermediate node and the first transceiver, the offset being in the direction of the second transceiver, receiving the timing packet by a second transceiver, the timing packet including the first field, information within the first field being at least based on the first offset, determining a second offset between the second transceiver and an intermediate node that provided the timing packet to the second transceiver and correcting a time of the second transceiver based on the information within the first field and the second offset.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/108,330, filed Dec. 1, 2020, entitled “Distributed Radio TransparentClock Over A Wireless Network,” now U.S. Pat. No. 11,381,490, which is acontinuation of U.S. patent application Ser. No. 16/566,747, filed Sep.10, 2019, entitled “Distributed Radio Transparent Clock Over A WirelessNetwork,” now U.S. Pat. No. 10,855,569, which is a continuation of U.S.patent application Ser. No. 16/046,948, filed Jul. 26, 2018, entitled“Distributed Radio Transparent Clock Over A Wireless Network,” now U.S.Patent Application No. 10,411,986, which claims priority to U.S.Provisional Patent Application Ser. No. 62/537,375 filed Jul. 26, 2017,and entitled “Distributed Radio Transparent Clock (DR-TC)” which arehereby incorporated by reference herein.

BACKGROUND 1. Field of the Invention(s)

The present invention(s) generally relate to transparent clocks across anetwork. More particularly, the invention(s) relate to systems andmethods for transparent clock signals across wireless network.

2. Description of Related Art

A Radio Transparent Clock (R-TC) can be employed to deliver highlyaccurate time using the IEEE 1588 protocol over microwave links. TheRadio Transparent Clock accounts for the packet delay variation andasymmetry of microwave link. Both quantities are crucial for IEEE 1588timing accuracy but unfortunately also an inherent property of microwaveradio interfaces.

Current synchronization techniques are capable of transferring frequencysynchronization across the physical layers used to transport the data(electrical, optical or wireless) but to achieve phase synchronizationalgorithms like IEEE 1588v2 may be utilized. Unfortunately, the phasesynchronization process at the packet level, as recommended by IEEE1588v2, imposes several restrictions and complexities if used acrosswireless links.

SUMMARY

An example method comprises receiving, by a first PHY of a firsttransceiver, a timing packet, timestamping, by the first transceiver,the timing packet and providing the timing packet to a firstintermediate node, receiving, by the first intermediate node, the timingpacket from the first transceiver, determining a first offset betweenthe first intermediate node and the first transceiver, updating a firstfield within the timing packet with the first offset between the firstintermediate node and the first transceiver, the offset being in thedirection of the second transceiver, receiving the timing packet by asecond transceiver, the timing packet including the first field,information within the first field being at least based on the firstoffset, determining a second offset between the second transceiver andan intermediate node that provided the timing packet to the secondtransceiver and correcting a time of the second transceiver based on theinformation within the first field and the second offset.

Determining the first offset between the first intermediate node and thefirst transceiver may comprise receiving, at the first intermediatenode, a request airframe from the first transceiver, the requestairframe including a first timestamp indicating a first time T1 that therequest airframe was transmitted from the first transceiver, the firsttransceiver and the second transceiver including a first and secondcounters, respectively, timestamping, by the first intermediate node, asecond time indication indicating a second time T2 that the requestairframe was received, generating a respond airframe and includingwithin the respond airframe a third time indication indicating a thirdtime T3 that the respond airframe is to be transmitted to the firsttransceiver, transmitting the respond airframe to the first transceiver,providing, by the first intermediate node, a timestamp informationrequest to the first transceiver, receiving a timestamp informationresponse, from the first transceiver, in response to the timestampinformation request, the timestamp information response including afourth time indication indicating a fourth time T4 when the respondpacket was received by the first transceiver, calculating, by the firstintermediate node, the first offset using the first time, second time,third time, and fourth time as follows:

${{counter}{offset}} = {\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2}.}$

In various embodiments, the first and second counters are synchronizedwith each other before the counter offset is calculated. The firsttransceiver and the second transceiver may have synchronizedfrequencies. The first counter may be a PTP counter.

In some embodiments, the method may further comprise determining betweenthe first transceiver and the first intermediate node asymmetry (ASY) inthe wireless link and calculating the counter offset includes

$\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2} \pm {\frac{Asy}{2}.}$

In some embodiments, the method may further comprise providing thetiming packet by the first intermediate node to a second intermediatenode, receiving, at the second intermediate node, a request airframefrom the first intermediate node, the request airframe including a firsttimestamp indicating a first time T1 that the request airframe wastransmitted from the first intermediate node, timestamping, by thesecond intermediate node, a second time indication indicating a secondtime T2 that the request airframe was received, generating a respondairframe and including within the respond airframe a third timeindication indicating a third time T3 that the respond airframe is to betransmitted to the first intermediate node, transmitting the respondairframe to the first intermediate node, providing, by the secondintermediate node, a timestamp information request to the firstintermediate node, receiving a timestamp information response, from thefirst intermediate node, in response to the timestamp informationrequest, the timestamp information response including a fourth timeindication indicating a fourth time T4 when the respond packet wasreceived by the first intermediate node, calculating, by the secondintermediate node, a third offset using the first time, second time,third time, and fourth time as follows:

${{{counter}{offset}} = \frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2}},$and updating the first field within the timing packet with the thirdoffset between the second intermediate node and the first intermediatenode, the third offset being in the direction of the second transceiver.

The second intermediate node may be the intermediate node that providedthe timing packet to the second transceiver. The method may furthercomprise determining between the second transceiver and the intermediatenode that provided the timing packet to the second transceiver,asymmetry (ASY) in the wireless link and calculating the counter offsetincludes

$\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2} \pm {\frac{Asy}{2}.}$Updating the first field within the timing packet with the first offsetbetween the first intermediate node and the first transceiver may beTS_(TLV)[i]=TS_(TLV)[i−1]+off_(TC) _(i+1) wherein the first field is aTLV and TS is timestamp and off is a first offset. The method mayfurther comprise the first transceiver updating the first field asfollows TS_(TLV)[1]=TS_(in)+off_(TC) ₂ .

In various embodiments, the second transceiver calculates a residencetime based on a time of the timing packet calculated at a PHY of thesecond transceiver and the information of the first field, as followsΔT_(res)=TS_(out)−TS_(TLV). The second transceiver may update a clockbased on the residence time as follows ΔT_(res)=TS_(out)−TS_(TLV).

An example system comprises a first transceiver, a first intermediatenode, and a second transceiver. The first transceiver may be configuredto receive, by a first PHY, a timing packet over an ethernet connection,a timing packet and timestamp the timing packet. The first intermediatenode may be configured to receive the timing packet from the firsttransceiver, determine a first offset between the first intermediatenode and the first transceiver, update a first field within the timingpacket with the first offset between the first intermediate node and thefirst transceiver, the offset being in the direction of the secondtransceiver. The second transceiver may be configured to receive thetiming packet, the timing packet including the first field, informationwithin the first field being at least based on the first offset,determine a second offset between the second transceiver and anintermediate node that provided the timing packet to the secondtransceiver and correct a time of the second transceiver based on theinformation within the first field and the second offset.

The first intermediate node configured to determine the first offsetbetween the first intermediate node and the first transceiver maycomprise the first intermediate node configured to receive a requestairframe from the first transceiver, the request airframe including afirst timestamp indicating a first time T1 that the request airframe wastransmitted from the first transceiver, timestamp a second timeindication indicating a second time T2 that the request airframe wasreceived, generate a respond airframe and including within the respondairframe a third time indication indicating a third time T3 that therespond airframe is to be transmitted to the first transceiver, transmitthe respond airframe to the first transceiver, provide a timestampinformation request to the first transceiver, receive a timestampinformation response, from the first transceiver, in response to thetimestamp information request, the timestamp information responseincluding a fourth time indication indicating a fourth time T4 when therespond packet was received by the first transceiver, and calculate, bythe first intermediate node, the first offset using the first time,second time, third time, and fourth time as follows:

${{counter}{offset}} = {\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2}.}$

The first intermediate node may be further configured to assist todetermine between the first transceiver and the first intermediate nodeasymmetry (ASY) in the wireless link and calculating the counter offsetincludes

$\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2} \pm {\frac{Asy}{2}.}$

In some embodiments, the system may further comprise a secondintermediate node, the second intermediate node configured to receivethe timing packet from the first intermediate node, receive a requestairframe from the first intermediate node, the request airframeincluding a first timestamp indicating a first time T1 that the requestairframe was transmitted from the first intermediate node, timestamp asecond time indication indicating a second time T2 that the requestairframe was received, generate a respond airframe and including withinthe respond airframe a third time indication indicating a third time T3that the respond airframe is to be transmitted to the first intermediatenode, transmit the respond airframe to the first intermediate node,provide a timestamp information request to the first intermediate node,receive a timestamp information response, from the first intermediatenode, in response to the timestamp information request, the timestampinformation response including a fourth time indication indicating afourth time T4 when the respond packet was received by the firstintermediate node, calculate a third offset using the first time, secondtime, third time, and fourth time as follows:

${{{counter}{offset}} = \frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2}},$and update the first field within the timing packet with the thirdoffset between the second intermediate node and the first intermediatenode, the third offset being in the direction of the second transceiver.

The second intermediate node may be the intermediate node that providedthe timing packet to the second transceiver. The second intermediatenode may be further configured to assist to determine between the secondtransceiver and the intermediate node that provided the timing packet tothe second transceiver, asymmetry (ASY) in the wireless link andcalculating the counter offset includes

$\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2} \pm {\frac{Asy}{2}.}$The first intermediate node may be configured to update the first fieldwithin the timing packet with the first offset between the firstintermediate node and the first transceiver asTS_(TLV)[i]=TS_(TLV)[i−1]+off_(TC) _(i+1) wherein the first field is aTLV and TS is timestamp and off is a first offset. The first transceivermay be further configured to update the first field as followsTS_(TLS)[1]=TS_(in)+off_(TC) ₂ .

An example method comprises receiving, at a first transceiver, a requestairframe from a second transceiver over a wireless link of a network,the request airframe including a first timestamp indicating a first timeT1 that the request airframe was transmitted to the first transceiver,the first transceiver and the second transceiver including a first andsecond counters, respectively, timestamping a second time indicationindicating a second time T2 that the request airframe was received,generating a respond airframe and including within the respond airframea third time indication indicating a third time T3 that the respondairframe is to be transmitted to the second transceiver, transmittingthe respond airframe to the second transceiver, providing, by the firsttransceiver, a timestamp information request to the second transceiver,receiving a timestamp information response, from the second transceiver,in response to the timestamp information request, the timestampinformation response including a fourth time indication indicating afourth time T4, calculating, by the first transceiver, a counter offsetusing the first time, second time, third time, and fourth time asfollows:

${{{counter}{offset}} = \frac{\left( {{TS1} + {TS4} - {TS3} - {TS2}} \right)}{2}},$calculating, by the first transceiver, a phase offset based on thecounter offset, and correcting, by the first transceiver, a phase of thefirst transceiver.

In various embodiments, the first and second counters are synchronizedwith each other before the counter offset is calculated. The firsttransceiver and the second transceiver may have synchronizedfrequencies. The first counter may be a PTP counter.

In some embodiments, the method further comprises determining asymmetry(ASY) in the wireless link and calculating the counter offset includes

$\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2} \pm {\frac{Asy}{2}.}$The first transceiver may generate and transmit the respond airframeimmediately after receiving the request airframe. The first transceivermay transmit the timestamp information request to the second transceiverat any time after the respond airframe is received.

The method may further comprise providing, by the second transceiver, atimestamp information request to the first transceiver, receiving atimestamp information response from the first transceiver, in responseto the timestamp information request, the timestamp information responseincluding at least the second time indication, calculating, by thesecond transceiver, a counter offset using the first time, second time,third time, and fourth time as follows:

${{{counter}{offset}} = \frac{\left( {{TS1} + {TS4} - {TS3} - {TS2}} \right)}{2}},$calculating, by the second transceiver, a phase offset based on thecounter offset, and correcting, by the second transceiver, a phase ofthe second transceiver. Calculating the phase offset by the firsttransceiver may not be synchronized with calculating the phase offset bythe second transceiver. The wireless link may be a microwave link.

Another example method includes generating, by a first transceiver, arequest airframe to be sent to a second transceiver over a wireless linkof a network, the request airframe including a first timestampindicating a first time T1 that the request airframe is to betransmitted by the first transceiver, the first transceiver and thesecond transceiver including a first and second counters, respectively,transmitting the request airframe to the second transceiver, receiving arespond airframe from the second transceiver, the respond airframeincluding within the respond airframe a third time indication indicatinga third time T3 that the respond airframe is to be transmitted to thefirst transceiver, determining a fourth time indication indicating afourth time T4 that the respond airframe was received, providing, by thefirst transceiver, a timestamp information request to the secondtransceiver, receiving a timestamp information response, from the secondtransceiver, in response to the timestamp information request, thetimestamp information response including a second time indicationindicating a second time T2 that the request airframe was received bythe second transceiver, calculating, by the first transceiver, a counteroffset using the first time, second time, third time, and fourth time asfollows:

${{{counter}{offset}} = \frac{\left( {{TS1} + {TS4} - {TS3} - {TS2}} \right)}{2}},$calculating, by the first transceiver, a phase offset based on thecounter offset, and correcting, by the first transceiver, a phase of thefirst transceiver.

The first and second counters may be synchronized with each other beforethe counter offset is calculated. The first transceiver and the secondtransceiver may have synchronized frequencies. The first counter may bea PTP counter. The method may further comprise determining asymmetry(ASY) in the wireless link and calculating the counter offset includes

$\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2} \pm {\frac{Asy}{2}.}$

The first transceiver may transmit the timestamp information request tothe second transceiver at any time after the respond airframe isreceived.

In various embodiments, the method may further comprise providing, bythe second transceiver, a timestamp information request to the firsttransceiver, providing a timestamp information response to the secondtransceiver, in response to the timestamp information request, thetimestamp information response including at least the third timeindication, calculating, by the second transceiver, a counter offsetusing the first time, second time, third time, and fourth time asfollows:

${{{counter}{offset}} = \frac{\left( {{TS1} + {TS4} - {TS3} - {TS2}} \right)}{2}},$calculating, by the second transceiver, a phase offset based on thecounter offset; and correcting, by the second transceiver, a phase ofthe second transceiver.

Calculating the phase offset by the first transceiver may not besynchronized with calculating the phase offset by the secondtransceiver.

An example system may comprise a first transceiver including memory anda processor, the first transceiver configured to: receive a requestairframe from a second transceiver over a wireless link of a network,the request airframe including a first timestamp indicating a first timeT1 that the request airframe was transmitted to the first transceiver,the first transceiver and the second transceiver including a first andsecond counters, respectively, timestamp a second time indicationindicating a second time T2 that the request airframe was received,generate a respond airframe and including within the respond airframe athird time indication indicating a third time T3 that the respondairframe is to be transmitted to the second transceiver, transmit therespond airframe to the second transceiver, provide a timestampinformation request to the second transceiver, receive a timestampinformation response, from the second transceiver, in response to thetimestamp information request, the timestamp information responseincluding a fourth time indication indicating a fourth time T4,calculate a counter offset using the first time, second time, thirdtime, and fourth time as follows:

${{{counter}{offset}} = \frac{\left( {{TS1} + {TS4} - {TS3} - {TS2}} \right)}{2}},$calculate a phase offset based on the counter offset, and correct aphase of the first transceiver.

Another example system may comprise a first transceiver including memoryand a processor, the first transceiver configured to: generate a requestairframe to be sent to a second transceiver over a wireless link of anetwork, the request airframe including a first timestamp indicating afirst time T1 that the request airframe is to be transmitted by thefirst transceiver, the first transceiver and the second transceiverincluding a first and second counters, respectively, transmit therequest airframe to the second transceiver, receive a respond airframefrom the second transceiver, the respond airframe including within therespond airframe a third time indication indicating a third time T3 thatthe respond airframe is to be transmitted to the first transceiver,determine a fourth time indication indicating a fourth time T4 that therespond airframe was received, provide a timestamp information requestto the second transceiver, receive a timestamp information response,from the second transceiver, in response to the timestamp informationrequest, the timestamp information response including a second timeindication indicating a second time T2 that the request airframe wasreceived by the second transceiver, calculate a counter offset using thefirst time, second time, third time, and fourth time as follows:

${{{counter}{offset}} = \frac{\left( {{TS1} + {TS4} - {TS3} - {TS2}} \right)}{2}},$calculate a phase offset based on the counter offset, and correct aphase of the first transceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example environment including transceiver radiofrequency units (RFU) in some embodiments.

FIG. 2 is an example air frame structure in some embodiments.

FIG. 3 depicts an environment including microwave link partners incommunication over microwave channel in some embodiments.

FIG. 4 depicts an example airframe exchange between a first transceiverand a second transceiver in some embodiments.

FIG. 5 depicts a data flow between the two transceivers in someembodiments.

FIG. 6 depicts an example transmitting radio frequency unit in someembodiments.

FIG. 7 is a block diagram of an example transceiver RFU in someembodiments.

FIG. 8 is an example diagram depicting a simplified Finite State Machine(FSM) as one of the possible implementations of the data exchangeprocess.

FIG. 9 depicts a flowchart for a distributed radio transparent clockacross nodes within a wireless network in some embodiments.

FIG. 10 depicts an example offset accumulation technique

DETAILED DESCRIPTION

Some embodiments described herein provide simple and accurate phase andfrequency synchronization across wireless links. Methods and systems aredescribed that detect phase variations across wireless links. Theproposed methodology may allow for the creation of a phase and frequencysynchronized wireless network.

Some embodiments described herein includes methods and techniques thatsimplify detection of phase variations over that described regardingIEEE 1588v2 and may, in some embodiments, improve the accuracy of thephase offset calculation. The phase offset calculation may be used forphase synchronization.

In some embodiments, a phase offset is calculated as a relativedifference between near-end and far-end units and is calculated on bothsides of the wireless link independently. In some embodiments, beforethe offset calculation is calculated, frequency synchronization iscompleted, and a time protocol counter may be at the data link layer oneach side of the wireless link. This application incorporates byreference US nonprovisional patent application titled “AirframeTimestamping Technique for Point-to-Point Radio Links,” filed Jul. 26,2018.

As discussed herein, the time protocol counter (e.g., precision timeprotocol (PTP)) on the data link layer on the near-end side of thewireless channel may be referred to as a “local time protocol counter”and the time protocol counter on the far-end side as a “remote timeprotocol counter.”

While embodiments described herein may refer to the IEEE 1588v2standard, it will be appreciated that embodiments described herein mayutilize many different standards and many different protocols. In someembodiments, examples will be described showing an improvement over theIEEE 1588 V2 standard. As discussed herein, various techniques may beutilized in place of or in addition to any number of different protocolsand standards (e.g., protocols and standards for frequencysynchronization).

Further, as discussed herein, a “unit” may refer to the whole systemconnecting to other systems either with wired or wireless links.

If there are any additional time protocol counter(s) (e.g., PTPcounters) on the unit (e.g., for timestamping Ethernet packets) thenmost or all of the time protocol counters (e.g., PTP counters) on eachunit may be synchronized with each other. In various embodiments, timeprotocol counter synchronization on the unit is done after frequencysynchronization process and before phase offset calculation process. Inone example, a local 1PPS signal may be used to synchronize local PTPcounters. It may not be relevant for some embodiments described hereinwhich time protocol counter is a source for time protocol countersynchronization. This can be system dependent and/or defined by higherlayer(s) of phase synchronization process. Further, initial phaseinformation and master-slave direction may not be relevant for thismethod/technique.

In some embodiments, higher layer(s) of the phase synchronizationprocess use the phase offset calculation of the particular wireless linkto transfer phase synchronization across this wireless link. Higherlayer(s) of the phase synchronization process may use the initial phaseinformation to properly perform phase synchronization relative to theinitial phase source. The higher layer(s) of the phase synchronizationprocess may be aware of master-slave direction, if needed, by clocktype. Direction change may be fast and simple as phase offsetcalculation may be simultaneously and independently available on eachside of the wireless link.

Examples of the method/technique may be capable of phase offsetcalculation across the data link layer used to handle blocks of datapacked into airframes (e.g., OSI layer 2). Airframes are used fortransferring blocks of data across wireless links. There is asignificant time variation between packets and how they are packed intoblocks of data of airframe. This is one of the reasons why phasesynchronization at the packet level does not perform as well for phasesynchronization across wireless links.

Different embodiments may include any number of the following advantagesover the 1588v.2 standard:

-   -   (1) Better precision and accuracy—two sides of the        point-to-point wireless link (e.g., two microwave routers        connected by a microwave radio link) may have better time        synchronization precision and accuracy by using methods        described herein compared to timestamping of packets at the        packet level (e.g., Ethernet packets). Packet level time        synchronization on the prior art introduces additional        scattering error (additional latency variation) as well as        additional deviation error (additional asymmetrical latency)        because there is a significant variable processing delay before        packets can be packed into airframes.    -   (2) Additional statistical precision may be gained through        averaging repeated measurements. With averaging measurement,        variations may be reduced or minimized due to cross-clock-domain        synchronization between asynchronous clock domains.    -   (3) The method/technique described herein may be independent of        the PTP master-slave configuration. In various embodiments, both        sides of the wireless point-to-point link calculate their own        phase offset (e.g., near-end side calculates phase offset        compared to far-end while far-end calculates its own phase        offset compared to near-end). The absolute values of both        offsets may be the same to the extent of measurement errors        while one is a positive value and the other is negative value.        This phase offset may be provided to the upper layer on both        sides regardless of master-slave configuration. The upper layer        may utilize the calculated phase offset in order to provide        transport of phase synchronization. The upper layer may be aware        of master-slave configuration, if needed, by clock type.        Direction change of master-slave configuration may be fast and        simple as phase offset calculation may be simultaneously and        independently available on each side of the wireless link.        However, the method/technique itself (or implementation of the        method/technique) may be independent of master-slave        configuration, which may make it an easier and more robust        solution compared to solutions that depend on master-slave        configuration.    -   (4) Independent of packet fragmentation. Various embodiments        described herein may be independent of packet payload data        including PTP timing packets (for IEEE 1588v2). When two or more        point-to-point radio links are used in parallel from one point        to another, then packet fragmentation (e.g., link aggregation        like L1LA) may be used over these parallel links to optimize        data traffic. This packet fragmentation process does not need to        be PTP IEEE 1588v2 aware.    -   (5) Unaffected user data bandwidth. Some embodiments described        herein may utilize transfer of local timestamps and other        required synchronization data between both sides of the wireless        link to calculate the phase offset. While timestamps required        for calculation may be taken close to each other with regards to        time, the transfer of this timestamp information between both        sides may not be time limited. Simple handshake may be used for        this information exchange within the data space for control        information, which may be available in every airframe, which may        not affect user data bandwidth (user traffic).

FIG. 1 depicts an example environment 100 including transceiver radiofrequency units (RFU) 102 and 104 in some embodiments. The transceiverRFUs 102 and 104 depicted in FIG. 1 are in wirelessly communication witheach other. In various embodiments, the transceiver RFUs 102 and 104communicate over microwave radio frequencies although it will beappreciated that transceiver RFUs 102 and 104 may communicate over anyportion of the wireless spectrum (e.g., not limited to the microwavespectrum).

Further, although depicted as communicating directly to each other, eachof the transceiver RFUs 102 and 104 may communicate via a tower or anyother receivers, transmitters, and/or transceivers.

The transceiver RFU 102 includes a first transceiver, a waveguide 106,and an antenna 108. The transceiver RFU 104 includes a firsttransceiver, a waveguide 110, and an antenna 112.

In various embodiments, the transceivers RFUs 102 and 104 may correctfor offset and phase utilizing systems and methods discussed herein.

The transmission over a microwave path may be based on a continuoussynchronous transmission of air frames separated by a preamble. FIG. 2is an example air frame structure 200 in some embodiments. Such atransmission scheme may be called a Constant Bit Rate (CBR).

In some embodiments, every air frame starts with the preamble 202 whichmay be a sequence known to the receiver. In this example, the preamble202 is followed by an Air Frame Link Control field 204, which containscontrol information defining the air frame 200. In various embodiments,the preamble 202 and the air frame link control field 204 are followedby blocks of QAM (or QPSK) symbols, called transport blocks (TB)206-216. Transport blocks (e.g., transport blocks 206-216) may becontainers for user data (e.g., Ethernet packets, TDM Payload, or thelike) and other required control data (e.g., ACM, ATPC, AGC, controlloops, or the like) exchanged mutually by microwave modems.

The size of those containers may depend on the current Adaptive CodingModulation (ACM) state and on the configured framing choice. Adaptivecoding modulation allows dynamic change of modulation and FEC level toaccommodate for radio path fading which is typically due to weatherchanges on a transmission path. Benefits of ACM may include improvedspectrum efficiency and improved link availability, particularly inwireless (e.g., microwave) links.

One of the disadvantages of changing the modulation level is that thischanges the throughput of the wireless (e.g., microwave) link. Suchchange on the wireless path (or any wireless path segment) causessignificant delay variation at the packet level. In one example, highPDV and asymmetry if the changes can occur only in one direction.Transport blocks (e.g., N*QAM Symbols) may also be used as theprocessing units for FFT operation and for further frequency domainprocessing. While discussion herein is directed to microwavecommunication, it will be appreciated that at least some embodiments anddiscussions herein may be applied to any wireless (e.g., radio frequency(RF)) communication.

The following includes some (not necessarily all) reasons for thecomplexity of obtaining exact timing of received and transmitted packetsat the physical level of a radio interface:

-   -   The microwave radio interface operates on a transport block        level as a basic data unit.    -   The transport block(s) require many stages of frequency and time        domain processing before the payload can be decoded.    -   Varying throughput due to ACM activity.

FIG. 3 depicts an environment 300 including microwave link partners 302and 304 in communication over microwave channel in some embodiments. Themicrowave link partners 302 and 304 may be or include transceivers,receivers, or transmitters. In some embodiments, the microwave linkpartner 302 may receive data to be transmitted over PHY 306.

The PHY 306 may be an Ethernet PHY (e.g., the data to be transmitted maybe received over an ethernet cable). The PHY 306 may process andmodulate the data into air frames (or any format) and provide themodulated data to the classification and routing module 308.

In various embodiments, systems and methods described herein utilizereceiving and providing data over Ethernet cable using an EthernetPhysical Layer device (e.g., PHY 306). Packets and/or PTP packets may bereceived from a switch or router. In various embodiments, the PHY 306may perform a timestamp at data ingress of the transceiver and PHY 314may perform a timestamp at data (e.g., the airframe) egress. Similarly,the PHY 322 of the second microwave link partner 304 may timestamp whendata (e.g., the airframe) is received over the microwave channel. Invarious embodiments, the PHY 330 may perform another timestamp ategress.

The classification and routing module 308 may direct data to betransmitted to the data packet queuing module 310 while directing datareceived from the radio frequency PHY 314 to the PHY 306. The datapacket and queuing module 310 may control data flow (e.g., bufferingand/or assist in load balancing) and provide the data to the schedulingmodule 312 which prepares the modulated data to be transmitted over theradio frequency PHY 314. The radio frequency PHY 314 may transmit thedata to another microwave link partner (e.g., microwave link partner304) and receive data. In various embodiments, the radio frequency PHY314 communicates over a microwave spectrum.

It will be appreciated that the microwave link partner (e.g., 302) maydown convert data (e.g., data received by a gigabit Ethernet PHY) toenable wireless transmission. The transceiver may up or down covert thedata to be transmitted (e.g., to an intermediate frequency where furtherprocessing may occur and then to an RF frequency for transmission).Further, there may be elastic buffers to transfer or change the dataspeed to a lower seed. As a result, phase and offset are increasinglydifficult to determine between devices across a wireless channel.Further, the radio may change modulation (e.g., in real-time).

The microwave link partner 304 may receive data from over the microwavechannel by the radio frequency PHY 322 which may provide the receiveddata to the classification and routing module 328 for routing andclassification of the received data to the PHY 330. The PHY 330 mayprovide the data to another digital device via Ethernet. Similar to themicrowave link partner 304,

The PHY 330 of the microwave link partner 304 may be an ethernet PHY(e.g., the data to be transmitted may be received over an ethernetcable). The PHY 330 may process and modulate the data into air frames(or any format) and provide the modulated data to the classification androuting module 328. The classification and routing module 328 may directdata to be transmitted to the data packet queuing module 326. The datapacket and queuing module 326 may control data flow (e.g., bufferingand/or assist in load balancing) and provide the data to the schedulingmodule 324 which prepares the modulated data to be transmitted over theradio frequency PHY 322. The radio frequency PHY 322 may transmit thedata to another microwave link partner (e.g., microwave link partner302) and receive data. In various embodiments, the radio frequency PHY322 communicates over a microwave spectrum.

Both microwave link partners 302 and 304 may include phase lock loops(PLLs) 316 and 322, respectively, to assist in recovery of clock signalsusing data received from over the wireless channel as described herein.The microwave link partners 302 and 304 may include system clocks 318and 334, respectively, that may include different time domains.

Offset and phase synchronization module 320 may determine offset andphase synchronization for the microwave link partner 302 based ontimestamps of the microwave link partners 302 and 304 as discussedherein. Similarly, offset and phase synchronization module 320 maydetermine offset and phase synchronization for the microwave linkpartner 304 based on timestamps of the microwave link partners 302 and304 as discussed herein.

FIG. 4 depicts an example airframe exchange between a first transceiver502 and a second transceiver 504 (e.g., microwave link partners 302 and304, respectively) in some embodiments. Airframes may be transferred inboth directions between local and remote sides with a constant airframeperiod. In this example, the local side will be referred to as the firsttransceiver 502 and the remote side will be referred to as the secondtransceiver 504. Also in this example, the wireless channel is amicrowave channel. FIG. 5 depicts a data flow between the twotransceivers 502 and 504 in some embodiments.

Timestamping of the airframe may be an independent process for radioegress and ingress directions and the timestamps. In variousembodiments, timestamps may be related to airframes rather than to anyspecific data inside data blocks. This enables the possibility to havefixed latency from the point of timestamp in the near-end modem, overthe air, to the point of timestamp in the far-end modem.

Phase offset between local and remote PTP counters on both sides ofpoint-to-point wireless link may be calculated using four timestampsbased on two airframes. To collect all four timestamps, the timestampingprocess of two airframes may be followed by a data exchange process. Forthe discussion herein, these two airframes may be named “request” and“respond” airframes.

In various embodiments, all airframes, regardless of how we call them,are intact from the traffic data point of view. The additional “channel”inside the airframe for may be utilized this method/technique. It may bedesired that this channel takes as little additional bandwidth aspossible. In the best case, it can be zero additional bandwidth if anexisting channel can be re-used.

In step 402, the first transceiver 502 may mark an airframe as a requestairframe 506. It will be appreciated that this airframe may be a PTPairframe, a time protocol airframe, or any other airframe.

In step 404, the first transceiver 502 (e.g., the radio frequency PHY314) timestamps the request airframe as TS1 and transmits the requestairframe 506 from the local side to the second transceiver (e.g., to theremote side (Unit 2) also called transceiver 504) of the point-to-pointwireless link. In some embodiments, the first transceiver 502 determinesa time TS1 and does not send the timestamp along with the requestairframe 506.

In step 406, the second transceiver 504 determines the time and maydetermine the time that the request airframe was received (TS2) 508.

In step 408, the second transceiver 504 may become the responding sideand may respond to this request by creating and transmitting an airframe(e.g., the first possible airframe) in the opposite direction. Theresponding airframe may be termed a “respond airframe” 510. The secondtransceiver 504 may determine a third time (TS3) that the respondairframe was sent. The second transceiver 504 may provide an indicationof TS2 or TS3 within the respond airframe.

In step 410, the first transceiver 502 may receive the respond air frameand determine a time that the respond airframe was received as TS4 512.

In some embodiments, the respond airframe follows the request airframeas soon as possible in order to minimize or reduce errors introduced bywander frequency of the whole system. Wander frequency has a typicalclock period of 100 ms while worst case delay between the request andrespond airframes is only a few milliseconds but could be less.

The data exchange process may follow the timestamping process. In someembodiments, this may be the required process to calculate the phaseoffset, however, it is not time critical. This means that timestamps andother required synchronization data from the responding side may betransferred to the requesting side through several airframes. This maybe done within an existing channel built inside the airframe fortimestamping purposes. Using the same channel may not be a requirementbut it may be desired so that no additional bandwidth is used.

In step 412, one side (e.g., the first transceiver or the secondtransceiver) may request time or counter data 514 from the other side(e.g., the first transceiver 502 may request synchronization data 514from the second transceiver 504 or the second transceiver 504 mayrequest synchronization data from the first transceiver 502) in step414. The responding side may mark the airframes (e.g., as “data”airframes). The receiving side may provide time indications thatindicate times that the requesting side does not have. For example, thesecond transceiver may provide, within a response to the request, timeindication indicating when the request airframe was received (TS2)and/or a time that the respond airframe was sent (TS3). Similarly, thefirst transceiver may provide time indication indicating when therequest airframe was sent (TS1) and/or a time that the respond airframewas received (TS4).

In step 416, the requesting side may calculate the offset (e.g., usingthe offset and phase synchronization module 320 or 336). In variousembodiments, offset is calculated on the requesting side aftercollecting the timestamps and other required synchronization data:

${Offset} = {\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2} \pm \frac{Asy}{2}}$

Any asymmetry on the round trip radio link path (marked as “Asy”)influences the calculation as seen from the formula. Asymmetry may bereduced, minimized, or eliminated with the possibility of characterizingand/or measuring each part in the radio link between both sides. If thisdata can be provided by hardware (HW), then no additional measurementsregarding asymmetry may be required.

Value(s) representing asymmetry may be introduced at the time ofestablishing the wireless link (e.g., preamble locking) while othervalue(s) (e.g., another part) may be introduced by having differentmodulations for radio egress and ingress directions of the selectedbandwidth.

Asymmetry may be calculated based on information from the modem abouttransmit and receive FIFOs. An FPGA may calculate the asymmetry.

In step 418, the requesting transceiver may correct phase based on theoffset (e.g., the Offset and phase synchronization module 320 or 336 maycorrect phase using the offset). In various embodiments, the calculatedphase offset information is a result at the physical layer and isfurther available to the higher layer. The higher layer may use thisphase offset information to transport the phase synchronization on thepacket level. The higher layer may also initiate the phase offsetcalculation process. There may be also the possibility that the higherlayer repeats this process in order to track any changes, especiallywhen modulations are changed.

FIG. 6 depicts an example transmitting radio frequency unit 602 in someembodiments. Although a transmitter is described in FIG. 6 , it will beappreciated that all or parts of the transmitter of FIG. 6 may be a partof the first transceiver 602 as discussed herein. In some embodiments,the transmitting radio frequency unit expresses components and a logicalflow of transmitting information over a wireless channel. Anytransceiver including any functionality may be utilized in performingall or part of the systems and/or methods described herein.

The transmitting radio frequency unit 602 (e.g., radio link partner 302or radio link partner 304) may comprise a modem module 604, apredistortion module 606, an adaptive module 608, mixer modules 610 and624, filter modules 612, 616, 626, and 630, oscillator modules 614 and628, a phase adjuster 618, an automatic gain control (AGC) module 620,amplification/attenuation module 622, a power amplifier 632, a signalquality module 634, waveguide filter 648, and waveguide 660.

In some embodiments, the transceiver 602 includes a digital signalprocessor (e.g., DSP). The DSP is any processor configured to provideone or more signals to the modem module 604. The digital signalprocessor (DSP) may comprise a digital signal processor, or anotherdigital device, configured to receiving a source signal intended fortransmission and converting the source signal to corresponding in-phase(I) and quadrature (Q) signals. For instance, the DSP may be implementedusing a digital device (e.g., a device with a processor and memory).Instructions stored on the storage system may instruct the DSP toreceive an input signal from a communications network interface, convertthe input signal to corresponding the in-phase (I) and quadrature (Q)signals, and provide the corresponding in-phase (I) and quadrature (Q)signals.

The modem module 604 may be any modem configured to receive one or moresignals to be transmitted. The modem module 604, in one example, mayreceive an in-phase (I) and quadrature (Q) signals and provide thesignals to the predistortion module 606. The modem module 604 maycomprise a modem device, or another digital device. The modem module 604may be configured to receive in-phase (I) and quadrature (Q) signals andmodulate the in-phase (I) and quadrature (Q) signals to encode theinformation.

The predistortion module 606 may receive the signal from the modemmodule 604 and improve the linearity of the signal. In variousembodiments, the predistortion module 606 inversely models gain andphase characteristics and produces a signal that is more linear andreduces distortion. In one example, “inverse distortion” is introducedto cancel non-linearity. The predistortion module 606 may receive apredistortion control signal based on a comparison of a signal from thepower amplifier 632. In one example, the predistortion module 606 mayreceive a signal based on the power amplifier 632 in order to adddistortion to an input signal to the power amplifier 632 to cancel(e.g., non-linear) noise generated by the power amplifier 632.

The adaptive module 608 may provide the predistortion control signalbased on the sample from the signal quality module 634 described herein.The predistortion module 606 may provide the I and Q signals to themixer module 610.

The mixer module 610, filter module 612, and the oscillator module 614may represent an upconverter configured to upconvert the signals to anintermediate frequency signal. Similarly, the mixer module 624, filtermodule 626, and oscillator module 628 also may represent an upconverterconfigured to further upconvert the signal to an RF signal. Thoseskilled in the art will appreciate that there may be any number ofupconverters configured to upconvert the signals within the transceiverradio frequency unit 602.

The mixer modules 610 and 624 may comprise mixers configured to mix thesignal(s) provided by the modem with one or more other signals. Themixer modules 610 and 624 may comprise many different types of mixerswith many different electrical properties. In one example, the mixer 610mixes I and Q signals received from the predistortion module 606 withthe filtered oscillating signal from the filter module 612 and theoscillator module 614. In another example, the mixer module 624 mixes asignal received from the amplifier/attenuator module 622 with thefiltered oscillating signal from the filter module 626 and theoscillator module 628.

The filter modules 612, 616, 626, and 630 may comprise filtersconfigured to filter the signal. The filter modules 612, 616, 626, and630 may comprise many different types of filters (e.g., bandpass filter,low pass filter, high pass filter, or the like) with many differentelectrical properties. In one example, the filter module 612 may be aband pass filter configured to filter the oscillation signal (orcomponents of the signal) provided from the oscillator module 614.Similarly, filter modules 612, 616, 626, and 630 may filter signals (orcomponents of the signals) from the oscillator module 614, theoscillator module 628, the mixer module 610, or the mixer module 624,respectively.

The oscillator modules 614 and 628 may comprise oscillators configuredto provide an oscillating signal that may be used to upconvert thesignal. The oscillator modules 614 and 628 may comprise any kind ofoscillator with any different electrical properties. In one example, theoscillator module 614 provides an oscillating signal to the filtermodule 612. The oscillator module 628 may provide an oscillating signalto the filter module 626.

The oscillator modules 614 and 628, either individually or together, maybe local or remote. In one example, the oscillating module 614 and/orthe oscillating module 628 may be remotely located and configured toprovide an oscillating signal to one or more transmitting radiofrequency units. In some embodiments, a single oscillating module mayprovide an oscillating signal to both the mixer module 610 and 624,respectively (e.g., optionally via a filter). In one example, theoscillator signal from the oscillator module may be altered (e.g.,oscillation increased or decreased) and provided to a different part ofthe circuit.

The signal quality module 634 may be configured to generate a phasecontrol signal to control the phase of a processed signal. In oneexample, the signal quality module 634 receives the upconverted RFsignal from the power amplifier 632 and mixes the signal with thefiltered oscillator signal or the upconverted signal from the secondupconverter (e.g., mixer module 624, filter module 626, and oscillatormodule 628). The signal quality module 634 may filter the signal andcompare the filtered, mixed signal with a predetermined phase value togenerate a phase control signal based on the comparison.

The phase adjuster 618 may comprise a variable phase control circuitconfigured to increase or decrease the phase of the signal to betransmitted. The phase adjuster 618 may comprise any different type ofphase adjuster or phase shifter with different electrical properties. Inone example, the phase adjuster 618 increases or decreases the phase ofthe signal received from the filter module 616. The phase adjuster 618may adjust the phase of the signal based on the phase control signalfrom the signal quality module 634.

The phase adjuster 618 may include one or more components. For example,the phase adjuster 618 may comprise one or more phase control elements.

The AGC module 620 may comprise an automatic gain control (AGC) circuitconfigured to increase or decrease the gain of the signal received fromthe phase adjuster 618. The AGC module 620 may comprise many differenttypes of AGCs with many different electrical properties. In one example,the AGC module 620 increases or decreases the gain of the signalreceived from the phase adjuster 618. The AGC module 620 may adjust thegain of the signal based on the gain control signal.

In various embodiments, in order to adjust the phase of the signal orthe amplitude of the signal, the signal quality module 634 may providecontrol signals to adjust the in-phase (I) and quadrature (Q) signals toachieve a desired adjustment. For example, in order to adjust the phaseor amplitude of the signal, the signal quality module 634 may utilizethe digital signal DSP to adjust the in-phase (I) and quadrature (Q)signals provided to the modem module 604 to achieve the desiredadjustment based on the predetermined phase value and/or thepredetermined amplitude value. In another example, in some embodiments,the signal quality module 634 may utilize the modem module 604 to adjustthe in-phase (I) and quadrature (Q) signals provided to thepredistortion module 606.

The amplification/attenuation module 622 may comprise an amplifierand/or an attenuator configured to amplify and/or attenuate a signal.The amplification/attenuation module 622 may be any kind of amplifier(s)and/or attenuator(s). Further, the amplification/attenuation module 622may comprise amplifiers and/or attenuators with any kind of electricalproperties. The power amplifier 632 may amplify the signal to betransmitted. It will be appreciated that the power amplifier 632 may addnoise to the signal to be transmitted (e.g., nonlinear noise) which maybe dynamically canceled through the addition of distortion in the signalto be transmitted by the predistortion module 606.

In some embodiments, the amplifier/attenuator module 622 receives asignal from the AGC module 620. The amplifier/attenuator module 622 mayamplify or attenuate the signal. Further, the power amplifier 632 mayamplify power of the signal (or components of the signal) after thesignal has been upconverted by the mixer module 624, the filter module626, and the oscillator module 628. The power amplifier 632 may thenprovide the signal to the signal quality module 634 and/or the waveguidefilter 648.

The transceiver radio frequency unit 602 may comprise the waveguidefilter 648, the waveguide 650, and/or a diplexer. The waveguide filter648 may be any filter coupled to the waveguide 650 and configured tofilter the electromagnetic waves (e.g., remove noise). The waveguide 650may provide the signal to the antenna via a diplexer. The diplexer mayprovide the signal to the antenna. Similar to the waveguide 646, thewaveguide 650 may be any waveguide kind or type of waveguide.

In various embodiments, by utilizing open loop calibration, the totalphase and amplitude for the whole transmitter path may be calibratedfrom I and Q input to the output of the power amplifier 632. In someembodiments, by calibration and look-up tables, the phase and amplitudemay be accurately detected, controlled, and set at the Tx outputdirectly or through adjusting I and Q signals at the input. The phaseoffset calculation, as discussed herein, may be processed at the PHYlevel (as opposed to the packet level). With PHY level processing, atleast some systems and methods described utilize the block data level(block level) of the airframe, the symbol level of the airframe, or anycombination of both.

Blocks of data may be mapped by the modem into symbols to be transmittedby the radio and are de-mapped by the modem using symbols received fromthe radio. The start of the airframe may be timestamped locally eitherat the block level or at the symbol level. In various embodiments, bothsides of a wireless link timestamp the airframe in the same manner toprovide a symmetrical environment from the time point of view.

FIG. 7 is a block diagram 700 of an example transceiver RFU 702 in someembodiments. Although a receiver is described in FIG. 7 , it will beappreciated that all or parts of the transmitter of FIG. 7 may be a partof the second transceiver 504 as discussed herein. In some embodiments,the receiving radio frequency unit 702 expresses components and alogical flow of transmitting information over a wireless channel. Anytransceiver including any functionality may be utilized in performingall or part of the systems and/or methods described herein.

Block diagram 700 comprises an antenna 704 and a diplexer 710 coupled tothe waveguide 706. The waveguide 706 may provide the signal from theantenna 704 to the diplexer 710 via a waveguide filter 708. The diplexer710 may provide the signal to the receiving radio frequency unit 702. Insome embodiments, the receiving radio frequency unit 702 may comprisethe waveguide 706, the waveguide filter 708, and/or the diplexer 710.

The waveguide 706 may be any waveguide kind or type of waveguide. Forexample, the waveguide 706 may be hollow or dielectric. In someembodiments, the waveguide 706 comprises a rectangular to circularwaveguide. The waveguide filter 708 may be any filter coupled to thewaveguide 706 and configured to filter the electromagnetic waves fromthe waveguide 706 (e.g., remove noise).

In various embodiments, the receiving radio frequency unit 702 isconfigured to receive a signal from the antenna 704 via the diplexer 710and adjust the phase of the received signal. The phase of the receivedsignal may be adjusted based on a comparison of the phase of the signaland a predetermined phase value. In some embodiments, the receivingradio frequency unit 702 may also be configured to adjust the gain ofthe received signal. In one example, the receiving radio frequency unit702 may adjust the gain of the received signal based on a comparison ofa gain of the received signal with a predetermined gain value.

The receiving radio frequency unit 702 may be any receiver including,but not limited to, a traditional heterodyne receiver with RXintermediate frequency (IF) output. Those skilled in the art willappreciate that multiple receiving radio frequency units may be used toreceive the same signal (e.g., signals containing the same informationprovided by a wireless communication source). Each receiving radiofrequency unit may adjust the phase of the received signal,respectively, based on the same predetermined phase value. Similarly,each receiving radio frequency unit may adjust the gain of the receivedsignal, respectively, based on the same gain value. As a result, thephase and gain of the signal from each receiving radio frequency unitmay be the same or substantially similar (e.g., the phase and gain ofthe signals may be identical). The signals may be subsequently combinedto strengthen the signal, increase dynamic range, and/or more accuratelyreproduce the information that was wirelessly transmitted.

The receiving radio frequency unit 702 may compriseamplification/attenuation modules and/or power amplifiers 712, 724, and738, filter modules 716, 720, 730, and 734 mixer modules 718 and 732,oscillator modules 722 and 736, phase control module 714, automatic gaincontrol modules 726, 740, and 742, and variable phase module 728.

The amplification/attenuation modules 712, 724, and 738 may comprise anamplifier and/or an attenuator configured to amplify and/or attenuate asignal. The amplification/attenuator modules 712, 724, and 738 may beany kind of amplifiers and/or attenuators. Further, theamplification/attenuator modules 712, 724, and 738 may each compriseamplifiers and/or attenuators with any kind of electrical properties.

In some embodiments, the amplifier/attenuator module 712 receives asignal via the antenna 704 and the diplexer 710. Theamplifier/attenuator module 712 may be a low noise amplifier configuredto amplify the signal (or components of the signal) before providing thesignal to the filter module 716 and the phase control module 714.Further, the amplifier/attenuator module 724 may attenuate the signal(or components of the signal) after the signal has been downconverted bythe mixer module 718, the filter module 720, and the oscillator module722. The amplifier/attenuator module 724 may then provide the signal tothe automatic gain control 726. The amplification/attenuator module 738may attenuate the signal (or components of the signal) after the signalhas been downconverted by the mixer 732, the filter module 734, and theoscillator module 736. The amplifier/attenuator module 738 may thenprovide the signal to the automatic gain control 740.

Those skilled in the art will appreciate that each of theamplifier/attenuator modules 712, 724, and 738 may be the same as one ormore other amplifier/attenuator modules. For example,amplifier/attenuator modules 712 and 724 may both be amplifiers sharingthe same electrical properties while amplifier/attenuator module 738 maybe an attenuator. In another example, amplifier/attenuator modules 712and 724 may both be amplifiers but have different electrical properties.

Each amplifier/attenuator module 712, 724, and 738 may include one ormore components. For example, the amplifier/attenuator module 712 maycomprise one or more amplifiers and/or attenuators.

The filter modules 716, 720, 730, and 734 may comprise filtersconfigured to filter the signal. The filter modules 716, 720, 730, and734 may comprise many different types of filters (e.g., bandpass filter,low pass filter, high pass filter, or the like) with many differentelectrical properties. In one example, the filter module 716 may be aband pass filter configured to filter the signal (or components of thesignal) received from the amplification/attenuation module 712 beforeproviding the signal to the mixer module 718. Similarly, filter modules720, 730, and 734 may filter signals (or components of the signals) fromthe oscillator module 722, the phase adjuster 728, and the oscillatormodule 736, respectively.

Those skilled in the art will appreciate that each of the filter modules716, 720, 730, and 734 may be the same as one or more other filtermodules. For example, filters module 716 and 720 may both be filterssharing the same electrical properties while filter module 730 may beanother kind of filter. In another example, filters module 716 and 720may both be filters of a similar type but have different electricalproperties.

Each filter modules 716, 720, 730, and 734 may include one or morecomponents. For example, the filter modules 716 may comprise one or morefilters.

The mixer modules 718 and 732 may comprise mixers configured to mix thesignal received from the antenna with one or more other signals. Themixer modules 718 and 732 may comprise many different types of mixerswith many different electrical properties. In one example, the mixer 718mixes a signal received from the filter module 716 with the filteredoscillating signal from the filter module 720 and the oscillator module722. In another example, the mixer module 732 mixes a signal receivedfrom the filter module 730 with the filtered oscillating signal from thefilter module 734 and the oscillator module 736.

Those skilled in the art will appreciate that each of the mixer modules718 and 732 may be the same as one or more other mixer modules. Forexample, mixer modules 718 and 732 may both be mixers sharing the sameelectrical properties or, alternately, the mixer modules 718 and 732 maybe another kind of mixer and/or with different electrical properties.

Each mixer modules 718 and 732 may include one or more components. Forexample, the mixer module 718 may comprise one or more mixers.

FIG. 8 is an example diagram depicting a simplified Finite State Machine(FSM) as one of the possible implementations of the data exchangeprocess. Note that timestamping of airframes is done in this examplewith regards to the state of the FSM and with regard to the receivedairframes.

Each side of wireless link may start its own process of phase offsetcalculation and that they may be independent between each other. Fromthe time point of view, they can start simultaneously or not. From thedata point of view, each side may collect its own timestamps forcalculating phase offset. It may not be relevant for thismethod/technique which side starts first.

Unlike optical or copper media, the physical layer of a radio interfaceis not aware of individual Ethernet packets, where an Ethernet packet isthe basic transmission unit transmitted on the physical layer. BothEthernet packets and airframes are basic transmission units in their ownmedium. From synchronization perspective, the airframe can be treated asa substitute for the Ethernet packet (e.g., PTP Sync message carryingtiming information). Joining microwave PHY specifics with existing a PTPtimestamping mechanism enables timestamping the airframe instead of theEthernet packet.

The transmission over a microwave path is typically based on acontinuous synchronous transmission of air frames separated by apreamble. As described herein, FIG. 2 is an example air frame structure200 in some embodiments. Such transmission scheme is also calledConstant Bit Rate (CBR). In some embodiments, every air frame startswith the preamble 202 which may be a sequence known to the receiver. Thepreamble 202 is followed by an Air Frame Link Control field 204, whichcontains control information defining the air frame 200. In variousembodiments, the preamble 202 and the air frame link control field 204are followed by blocks of QAM (or QPSK) symbols, called transport blocks(TB) 206-216. Transport blocks (e.g., transport blocks 206-216) may becontainers for user data (e.g., Ethernet packets, TDM Payload, or thelike) and other required control data (e.g., ACM, ATPC, AGC, controlloops, or the like) exchanged mutually by microwave modems.

The size of those containers may depend on the current Adaptive CodingModulation (ACM) state and on the configured framing choice. Adaptivecoding modulation allows dynamic change of modulation and FEC level toaccommodate for radio path fading which is typically due to weatherchanges on a transmission path. Benefits of ACM may include improvedspectrum efficiency and improved link availability, particularly inwireless (e.g., microwave) links.

One of the disadvantages of changing the modulation level is changingthe throughput of the microwave link. Such change on the microwave path(or any microwave path segment) causes significant delay variation atthe packet level. In one example, high PDV and asymmetry if the changescan occur only in one direction.

Additional factors contributing PDV and asymmetry, related to ACM, isthe use of frequency division duplex (FDD) scheme, which is commonpractice of any modern microwave modem. Because of the FDD scheme, it islikely that one direction is more impacted by the radio path fading thanthe other. Hence the ACM shift can occur only in one direction. If theACM shift occurs only in one direction the magnitudes of PDV andasymmetry are even higher and more disruptive for the synchronization.Yet a further contributing factor related to ACM is in its dynamics. Asdiscussed above, the dynamics of ACM activity are a consequence ofenvironmental change in order to accommodate for radio path fading. Assuch the ACM activity is hard or even impossible to predict and thataffects also the effectiveness of algorithms that strive to eliminate(to compensate and/or to filter out) the impact of ACM onsynchronization performance.

Between the microwave PHY and MAC layers there may also be packetbuffers (FIFOs) to allow data rate adjustments between these two planes.Packet buffering additionally distorts packet timing information, thuscauses additional PDV. Ethernet packets are processed at the MAC layerwhere they were already exposed to all of the above mentioneddisturbances. Thus, the timing information in the PTP synchronizationpacket obtained at the MAC layer of the radio interface is consequentlyalready distorted as well. This means that the precise and accuratetimestamping of the PTP packet, which is the main advantage of PTP inachieving high synchronization accuracy, has no benefit if thetimestamping is performed at the MAC level of a radio interface.

Phase/time accuracy measurements performed with various PTP slaves fromdifferent vendors show that even advanced state of the art packetfiltering algorithms employed on a PTP slave without explicit in-depthknowledge about the given radio PHY and its current state, show littleimprovement on synchronization accuracy. Without adequate full on-pathsupport from the microwave system packet filtering algorithms,implemented on a PTP Slave, cannot guarantee that the net error,introduced by single MW link, will be below 1.1 μs. The 1.1 μs is thehighest targeted budget for network equipment (excluding budgets forPRTC/GM, end Slave device and holdover) specified by ITU-T [2] in orderto support mobile communication technologies like LTE-TDD. Thetechnology like LTE-A, 5G and beyond requires an even more stringentphase/time accuracy which goes down to 500 ns and even below 100 ns forspecial applications (MIMO, Location Services, CA and CoMP between anytwo stations in the network).

Based on the foregoing, it is clear that the MAC layer of a radiointerface and layers above it cannot provide adequate timing informationrequired for precise synchronization.

In reviewing signals related to the PHY level of the radio interface onvarious radio modems from different vendors, the most relevant timingsignals that can be used appear to be those indicating individual symboland/or group of symbols like start of AF or preamble signal.

Unfortunately, the accessibility of such signals and the level at whichthey are accessible in practice varies with different PHYimplementations and with different PHY vendors. For that reason, it isimpossible to generalize the approach of exploiting native timingsignals present in the microwave radio PHY. Exploiting those signalsrequires an in-depth explicit knowledge of the given PHY implementationand the way such timing signals are accessed. Especially it is importantto know all the elements contributing to the transmit and receive PHYlatency at the level of the accessed timing signal. Such elements areFIFOs (and its depth variation) in transmit and receive path,modulator/demodulator latency, digital filters, equalizers and other DSPblocks. The accurate transmit and receive PHY latencies are essentialparameters needed for the estimation of the PHY asymmetry. Withoutexplicit knowledge about the PHY latencies (i.e. being able to measureit or estimate it), even the timing signals, accessed on a PHY level,per se cannot satisfy requirements for precise synchronization.

The following includes some (not necessarily all) reasons for thecomplexity of obtaining exact timing of received and transmitted packetsat the physical level of a radio interface:

-   -   The microwave radio interface operates on a transport block        level as a basic data unit.    -   The transport block(s) require many stages of frequency and time        domain processing before the payload can be decoded.    -   Varying throughput due to ACM activity.

In various embodiments, to overcome one or more of the above-mentionedMAC level disadvantages, a Distributed Radio Transparent Clock (DR-TC)may enable accurate time transport over wireless (e.g., microwave) linksleveraging the widely adopted IEEE1588 protocol.

In some embodiments, one aspect of the developed DR-TC may be the use ofaccurate timing information obtained at the PHY layer of a microwaveradio interface for the calculation of the required correction toIEEE1588 timing packets (correction field update calculation).

The DR-TC is a distributed Transparent Clock with Ethernet interfaces onthe edges and one or more wireless links (e.g., MW/mmW links)interconnecting them. In some embodiments, on the edges the DR-TCtime-stamps the ingress PTP timing packets and/or appends the timestampdata in a designated type, length value (TLV) field of the PTP timingpacket.

In one example, the timestamp data represents the acquired packettimestamp corrected with the time offset value measured in a directiontowards the remote MW link partner.

The local to remote offset may be the time difference between twoindependently synchronized (e.g., SyncE) counters running on both sidesof the radio link. Correction of the acquired timestamp thereforerepresents a transformation of the captured timestamp in the time domainof the remote radio link partner. Further traversing of PTP timingpackets over microwave nodes of DR-TC does not involve additional packettime-stamping on subsequent nodes. Instead of packet time-stamping ateach subsequent node, the DR-TC may update the time-stamp data insidethe designated TLV with the time offset value measured in a directiontoward remote MW link partner.

This process may be repeated on all intermediate microwave nodes. On theegress, the DR-TC again time-stamps the timing packets (e.g., PTP timingpackets) and calculates the resident time based on the acquired egresspacket timestamp and the time-stamp data from the designated TLV. TheDR-TC further performs the final timing packet (e.g., PTP) correctionfield update with the calculated resident time and removes the appendedTLV. Example DR-TC calculations are shown herein where the remote offsetis input data for the DR-TC processing.

In various embodiments, to overcome one or more of the above-mentionedMAC level key disadvantages of microwave PHY, a Distributed RadioTransparent Clock may enable accurate time transport over microwavelinks using (e.g., leveraging) aspects of the widely adopted IEEE1588protocol.

At least one aspect of the developed DR-TC is the use of accurate timinginformation obtained at the PHY layer of the microwave radio interfacefor the calculation of the required correction to the IEEE1588 timingpackets (Correction field update calculation).

The timestamp data represents the acquired packet timestamp correctedwith the time offset value measured in a direction towards the remote MWlink partner. The local to remote offset may be the time differencebetween two independently synchronized (SyncE assumed) counters runningon both sides of the radio link. Correction of the acquired timestamptherefore represents a transformation of the captured timestamp in thetime domain of the remote radio link partner.

Further traversing of PTP timing packets over 1\4 W nodes of DR-TC doesnot involve additional packet time-stamping on subsequent nodes. Insteadof packet time-stamping at each subsequent node, the DR-TC may updatethe time-stamp data inside the designated TLV with the time offset valuemeasured in a direction toward remote MW link partner. This process maybe repeated on all intermediate MW nodes (see equation [2] below). Onthe egress, the DR-TC again may time-stamp the PTP timing packets andcalculates the resident time based on the acquired egress packettimestamp and the time-stamp data from the designated TLV (see equation[3] below). The DR-TC further performs the final PTP correction fieldupdate with the calculated resident time and removes the appended TLV.The required DR-TC calculations are show in equations 1-3. In someembodiments, it may be assumed that the remote offset is an input datafor the DR-TC processing.ΔT _(resident)=TS_(out)−TS_(in) ΔT _(resident)=TS_(out)−TS_(in)  [1]ΔT _(resident)=TS_(out)−(TS_(in)+Σ_(i=1) ^(N)off_(TC) _(i+1) )  [2]CF _(new) =CF _(old) +ΔT _(resident)  [3]

In various embodiments, with the use of the signalization and datachannel for timestamp data exchange discussed herein, a “pseudo”peer-delay measurement mechanism at the airframe level purely inhardware may be implemented. In one example, the mechanism may enableacquisition of four timestamps required to calculate the airframepropagation delay and time offset between the local and remote radioPHYs.

In some embodiments, software control may be used to acquire all fourtimestamps. The software may be responsible for triggering thetimestamping mechanism, collecting the acquired timestamp data andcalculating airframe propagation delay and time offset between the localand remote sides. Additionally, the software may also responsible forthe link asymmetry compensation.

The PHY asymmetry and PHY components contributing to the asymmetryvaries based on what level of the PHY the timing signals may beaccessed. In this example, the timestamping point may be placed at thelevel where the airframe is assembled and disassembled (e.g., framer).At this point the FEC blocks, modulator, and demodulator blocks and allDSP blocks may be enveloped by timestamp boundaries. In someembodiments, the transmit and receive PHY latencies are both dependentupon the given modulation scheme. The components contributing to theasymmetry may be the transmitting and receiving FIFO depths and latencythrough the modulator/demodulator, all dependent upon modulation.

The receive FIFO depth may be additionally dependent on the respectivelink acquisition while the transmit FIFO depth may be additionallychanged every time the transmitter chain is reinitialized. Both FIFOlevels may be provided by the modem itself. Based on FIFO levels, thesoftware may calculate the link asymmetry. With the calculatedasymmetry, the software may then further improve the accuracy of thepreviously calculated airframe propagation delay and time offset betweenradio link partners. All four airframe timestamps along with the FIFOlevels and PHY latencies (e.g., measured with an FPGA) provided to thesoftware may produce the time offset between the radio link partnerswhich may be compensated for estimated PHY asymmetry. In one example,measured PHY asymmetry in case of BCM85620 ranges from few tens of ns tofew μs. This clearly shows that without explicit knowledge about PHYlatencies even the timing signals, accessed at the PHY level, on theirown cannot satisfy requirements for precise synchronization. Theasymmetry compensated time offset may be additionally filtered with alow pass filter and averaged (e.g., using a simple moving average).Filtering and averaging are needed to suppress spikes originated fromthe timestamping granularity of 8 ns and the clock domain crossingbetween the AF timestamping unit and the AF preamble signal. The finalfiltered time offset may then taken by a Network Processor (NP) wherethe PTP protocol level of the novel DR-TC functionality may beimplemented.

FIG. 9 depicts a flowchart for a distributed radio transparent clockacross nodes within a wireless network in some embodiments. FIG. 10depicts an example offset accumulation technique. In variousembodiments, a distributed PTP Transparent Clock implementation thatencapsulates a microwave link or a chain of microwave links and forms aPTP Transparent clock between the Ethernet interfaces on the edges. FIG.10 depicts first transceiver 1008 in wireless communication with thesecond transceiver 1014 over wireless links 1002, 1004, and 1006 viaintermediate nodes 1010 and 1012. The intermediate nodes may include oneor more transceivers. The intermediate nodes are any devices (e.g.,including memory and a processor) capable of receiving and relayinginformation across wireless links.

As discussed regarding FIG. 4 , each transceiver and intermediate nodemay determine or assist in determining an offset within a wireless linkbetween itself and another device. Similarly, each transceiver andintermediate node may determine or assist in determining asynchronousperformance within a wireless link between itself and another devicewhich may be utilized to assist in determining one or more offsets.

The DR-TC exploits the previously discussed mechanism of airframetimestamping that results in a calculated time offset between the localand remote sides of the radio link. The DR-TC additionally may exploitthe offset accumulation technique described herein and the PHY layerfrequency transport by means of SyncE.

In some embodiments, the high level principle of DR-TC is to transporttime protocol (e.g., PTP) packet timestamps from one edge to anotheredge across a frequency synchronized (e.g., SyncE) microwave systemwhere the microwave system (chain of DR-TC nodes) may not be phase ortime aligned. The phase/time on every microwave DR-TC node may bearbitrary and uncorrelated with other nodes. The DR-TC may transformingress timestamps from an Ethernet interface on one edge into a timedomain of egress timestamps on the Ethernet interface on the other edge.The timestamp transformation from one edge to the other along the chainof DR-TC nodes may be performed partially on every intermediate DR-TCnode. The end-to-end transformation of the ingress timestamps into atime domain of egress timestamps may be achieved by accumulating partialtransformations; this is the accumulation (summation) of individual timeoffsets calculated between radio link partners on every DR-TC node alongthe chain. The end DR-TC node uses this transformed ingress timestampalong with its egress timestamp to calculate the packet residence time.

From the time protocol (e.g., PTP) packet perspective, the DR-TC timestamps the ingress timing packets on one edge and appends thetransformed timestamp in a designated TLV of a timing (e.g., PTP)packet. While PTP packets are discussed herein, it will be appreciatedthat any time protocol packet may be utilized.

Further, although packets are described herein, it will be appreciatedthat any time protocol airframe or other container for providing dataacross the wireless link(s) may be utilized.

In one example, the first transceiver 1008 timestamps (e.g., providestime indicating in timestamp or time) ingress timing packets at a PHY(e.g., PHY 306 of microwave link partner 302) in step 902. In step 904,the first transceiver 1008 appends the transformed timestamp in a TLVfield of the timing packet. Although the TLV field is described herein,it will be appreciated that any field may be utilized. Here thetransformed timestamp may represent the acquired packet timestampcorrected with the time offset value measured in a direction towards theremote radio link partner (DR-TC 2 or second transceiver 1018).TS_(TLV)[1]=TS_(in)+off_(TC) ₂   (1)

In step 906, an intermediate node may receive a timing packet.

In step 908, the intermediate node may determine an offset. In someembodiments, the intermediate node 1010 may receive the timing packetand may determine an offset using the method described regarding FIG. 4for determining an offset. For example, the intermediate node 1010 mayreceive a request packet including an indication of a first time (TS1)the request packet was sent from the first transceiver 1008, determinean indication of a second time (TS2) when the request packet wasreceived, generate a respond packet, determine an indication of a thirdtime (TS3) when the respond packet is sent to the first transceiver1008, request time data from the first transceiver 1008, receive aresponse including at least an indication of a fourth time (TS4), anddetermine an offset using TS1, TS2, TS3, and TS4 (and/or asynchronousnetwork performance) as discussed herein.

To continue the discussion in the context of FIG. 10 , the intermediatenode 1012 may receive the timing packet from intermediate node 1010 andmay determine an offset using the method described regarding FIG. 4 fordetermining an offset. For example, the intermediate node 1012 mayreceive a request packet including an indication of a first time (TS1)the request packet was sent from the intermediate node 1010, determinean indication of a second time (TS2) when the request packet wasreceived, generate a respond packet, determine an indication of a thirdtime (TS3) when the respond packet is sent to the intermediate node1010, request time data from the intermediate node 1010, receive aresponse including at least an indication of a fourth time (TS4), anddetermine an offset using TS1, TS2, TS3, and TS4 (and/or asynchronousnetwork performance) as discussed herein.

Further traversing of timing packets over radio nodes of the DR-TC doesnot involve additional packet time stamping on subsequent nodes.Instead, at each subsequent node (e.g., node 1010 and 1012, the DR-TC(e.g., each node 1010 and 1012) updates (add to the previous sum) thetime-stamp data inside the designated TLV with the time offset valuemeasured in a direction toward remote radio link partner in step 910.TS_(TLV) [i]=TS_(TLV) [i−1]+off_(TC) _(i+1)   (2)

This process is repeated on all intermediate radio nodes 912. For NDR-TC nodes, the end-to-end TS_(TLV) transformation is as follows:TS_(TLV) [N]=TS_(in)+Σ_(i=1) ^(N-1)off_(TC) _(i+1)

On timing packet egress, the DR-TC (e.g., the second transceiver 1014 ortarget node) again time-stamps the PTP timing packets and calculates theresidence time ΔT_(res) based on the acquired egress PTP packettimestamp TS_(out) and transformed time-stamp data TS_(TLV) from thedesignated TLV in step 914. In various embodiments, the secondtransceiver 1014 may determine an offset based on time indicationsbetween itself and the last node in communication with the secondtransceiver 1014 (e.g., intermediate node 1012). The offset may be addedor combined with the value(s) in the TLV and used to assist incalculating equation 3.ΔT _(res)=TS_(out)−TS_(TLV)  (3)

The DR-TC at the end point performs the final step; updates PTPcorrection field with the calculated residence time in step 916, seeequation (4), and removes appended TLV.CF _(new) =CF _(old) +ΔT _(res)  (4)

In various embodiments, the second transceiver may update a counter orclock using the result from equation (4). Similarly, intermediate nodesmay update their counter, clock, and/or phase using the offsetinformation and possibly information from the TLV field (as well asinformation regarding asynchronous behavior in any or all of thewireless links). Further, the second transceiver may update its phasebased on an offset determined between the second transceiver and thelast intermediate node that provided data directly to the secondtransceiver.

It will be appreciated that microwave is the most dominant technologyglobally for building high capacity backhaul to support mobile networks.In some embodiments, the concept of DR-TC may enable seamless phase/timesynchronization transport over microwave networks with nanosecondaccuracy. Discussed herein are example offset accumulation techniqueemployed as part of the DR-TC concept, which additionally removes theneed for prior phase/time alignment of the whole microwave system. Thismeans that there is no need to run and build any kind of Master-Slavehierarchy for phase/time transportation across the whole microwavesystem. Instead, peer offset between every radio link partner may becontinuously measured and monitored on every DR-TC node, similar to thePTP peer delay mechanism. This means that the DR-TC is “transparent” tothe actual PTP Master-Slave direction. As a result, the DR-TC is able toquickly adapt after path reconfiguration which is especially importantin complex topologies like rings or partial mesh.

The above-described functions and components can be comprised ofinstructions that are stored on a storage medium such as a computerreadable medium. The instructions can be retrieved and executed by aprocessor. Some examples of instructions are software, program code, andfirmware. Some examples of storage medium are memory devices, tape,disks, integrated circuits, and servers. The instructions areoperational when executed by the processor to direct the processor tooperate in accord with some embodiments. Those skilled in the art arefamiliar with instructions, processor(s), and storage medium.

Various embodiments are described herein as examples. It will beapparent to those skilled in the art that various modifications may bemade and other embodiments can be used without departing from thebroader scope of the present invention. Therefore, these and othervariations upon the exemplary embodiments are intended to be covered bythe present invention(s).

The invention claimed is:
 1. A method comprising: receiving, by a firsttransceiver, data over a wired connection; packaging the data into aparticular airframe; timestamping, by a first physical layer of thefirst transceiver, the particular airframe; providing, by the firsttransceiver, the particular airframe to a first intermediate node;receiving, by the first intermediate node, the particular airframe fromthe first transceiver; determining a first offset between the firstintermediate node and the first transceiver; updating a first fieldwithin the particular airframe with the first offset between the firstintermediate node and the first transceiver; receiving the particularairframe by a second transceiver, the particular airframe including thefirst field; determining a second offset between the second transceiverand an intermediate node that provided the particular airframe to thesecond transceiver; and correcting a time of the second transceiverbased on information within the first field and on the second offset,the information in the first field being based on the first offset. 2.The method of claim 1, wherein determining the first offset between thefirst intermediate node and the first transceiver comprises: determiningby the first transceiver a first indication indicating a first time TS1that a request airframe was transmitted from the first transceiver tothe first intermediate node, the first transceiver and the firstintermediate node including first and second counters, respectively;determining by the first intermediate node a second time indicationindicating a second time TS2 that the request airframe was received bythe first intermediate node; determining by the first intermediate nodea third time indication indicating a third time TS3 that a respondairframe is being transmitted to the first transceiver; determining bythe first transceiver a fourth time indication indicating a fourth timeTS4 when the respond airframe was received by the first transceiver; andcalculating the first offset using the first time, the second time, thethird time, and the fourth time.
 3. The method of claim 2, where thefirst and second counters are synchronized with each other before thefirst offset is calculated.
 4. The method of claim 2, wherein the firstcounter is a Precision Time Protocol (PTP) counter.
 5. The method ofclaim 2, further comprising determining asymmetry (ASY) in a wirelesslink between the first transceiver and the first intermediate node,wherein calculating the first offset includes$\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2} \pm {\frac{Asy}{2}.}$6. The method of claim 2, further comprising: determining by the firstintermediate node a fifth indication indicating a fifth time TS5 that asecond request airframe was transmitted from the first intermediate nodeto a second intermediate node; determining by the second intermediatenode a sixth time indication indicating a sixth time TS6 that therequest airframe was received by the second intermediate node;determining by the second intermediate node a seventh time indicationindicating a seventh time TS7 that a second respond airframe is beingtransmitted to the first intermediate node; determining by the firstintermediate node an eighth time indication indicating an eighth timeTS8 when the second respond airframe was received by the firstintermediate node; and calculating a third offset using the fifth timeindication, the sixth time indication, the seventh time indication, andthe eighth time indication; and updating the information within thefirst field with the third offset between the second intermediate nodeand the first intermediate node.
 7. The method of claim 6, wherein thesecond intermediate node is the intermediate node that provided theparticular airframe to the second transceiver.
 8. The method of claim 7,further comprising determining asymmetry (ASY) in a wireless linkbetween the second transceiver and the intermediate node that providedthe particular airframe to the second transceiver, wherein calculatingthe third offset includes$\frac{\left( {{{TS}5} + {{TS}6} - {{TS}7} - {{TS}8}} \right)}{2} \pm {\frac{Asy}{2}.}$9. The method of claim 1, wherein the first transceiver and the secondtransceiver have synchronized frequencies.
 10. The method of claim 1,wherein the updating the information within the first field with thefirst offset between the first intermediate node and the firsttransceiver is TS_(TLV) [i]=TS_(TLV) [i−1]+off_(TC) _(i+1) wherein thefirst field is a TLV, TS is a timestamp, and off is the first offset.11. The method of claim 10, further comprising updating the informationwithin the first field as follows: TS_(TLV) [1]=TS_(in)+off_(TC) ₂ . 12.The method of claim 11, wherein the second transceiver calculates aresidence time based on a time of the particular airframe calculated ata physical layer of the second transceiver and the information of thefirst field, as follows: ΔT_(res)=TS_(out)−TS_(TLV).
 13. The method ofclaim 12, wherein the second transceiver updates a clock based on theresidence time as follows: ΔT_(res)=TS_(out)−TS_(TLV).
 14. The method ofclaim 1, wherein the intermediate node that provided the particularairframe to the second transceiver is the first intermediate node.
 15. Asystem comprising: a first transceiver configured to receive data over awired connection, configured to package the data into a particularairframe, and configured to timestamp the particular airframe; a firstintermediate node configured to receive the particular airframe from thefirst transceiver, configured to determine a first offset between thefirst intermediate node and the first transceiver, and configured toupdate a first field within the particular airframe with the firstoffset between the first intermediate node and the first transceiver;and a second transceiver configured to receive the particular airframeby a second transceiver, the particular airframe including the firstfield, configured to determine a second offset between the secondtransceiver and an intermediate node that provided the particularairframe to the second transceiver, and configured to correct a time ofthe second transceiver based on information within the first field andon the second offset, the information in the first field being based onthe first offset.
 16. The system of claim 15, wherein the firsttransceiver configured to determine the first offset between the firstintermediate node and the first transceiver comprises the firsttransceiver configured to calculate the first offset using a first timeTS1, a second time TS2, a third time TS3, and a fourth time TS4, thefirst time TS1 being a first indication indicating when a requestairframe was transmitted from the first transceiver to the firstintermediate node, the first transceiver and the first intermediate nodeincluding first and second counters, respectively, the second time TS2being a second time indication indicating when the request airframe wasreceived by the first intermediate node, the third time TS3 being athird time indication indicating when a respond airframe is beingtransmitted to the first transceiver, the fourth time TS4 being a fourthtime indication indicating when the respond airframe was received by thefirst transceiver.
 17. The system of claim 16, the first intermediatenode being further configured to assist to determine asymmetry (ASY) ina wireless link between the first transceiver and the first intermediatenode and to calculate the first offset using$\frac{\left( {{{TS}1} + {{TS}4} - {{TS}3} - {{TS}2}} \right)}{2} \pm {\frac{Asy}{2}.}$18. The system of claim 16, further comprising a second intermediatenode, the second intermediate node configured to receive the timingpacket from the first intermediate node, the first intermediate nodeconfigured to calculate a third offset using a fifth time TS5, a sixthtime TS7, a seventh time TS8, and an eighth time TS8 as follows:${{{third}{offset}} = \frac{\left( {{{TS}5} + {{TS}6} - {{TS}7} - {{TS}8}} \right)}{2}},$the fifth time TS5 being a fifth indication indicating when a secondrequest airframe was transmitted from the first intermediate node to thesecond intermediate node, the sixth time TS6 being a second timeindication indicating when the second request airframe was received bythe second intermediate node, the seventh time TS7 being a seventh timeindication indicating when a second respond airframe is beingtransmitted to the first intermediate node, the eighth time TS8 being aneighth time indication indicating when the second respond airframe wasreceived by the first intermediate node.
 19. The system of claim 18,wherein the second intermediate node is the intermediate node thatprovided the timing packet to the second transceiver.
 20. The system ofclaim 19, wherein the first intermediate node is further configured toassist to determine asymmetry (ASY) in a wireless link between thesecond transceiver and the intermediate node that provided the timingpacket to the second transceiver and to calculate the third offset using$\frac{\left( {{{TS}5} + {{TS}6} - {{TS}7} - {{TS}8}} \right)}{2} \pm {\frac{Asy}{2}.}$21. The system of claim 15, wherein the first transceiver is configuredto update the information within the first field within the timingpacket with the first offset between the first intermediate node and thefirst transceiver as TS_(TLV) [i]=TS_(TLV) [i−1]+off_(TC) _(i+1) whereinthe first field is a TLV, TS is a timestamp, and off is the firstoffset.